The present invention relates to a process for the production of a matrix of electronic components. It applies to any matrix-type arrangement of electronic components and particularly a matrix of elements used for controlling a liquid crystal or electroluminescent display screen, or optical detectors.
In a matrix of electronic components having m rows and n columns of components which are electrically interconnected, the excitation of a component ij located at the intersection of the row i, i being an integer such that 1.ltoreq.i.ltoreq.m, and column j, j being an integer such that 1.ltoreq.j.ltoreq.n, is carried out by simultaneously exciting (applying a voltage) row i and column j of components.
The selective control of this electronic component is only possible if the components have a sufficiently non-linear characteristic permitting multiplexing.
In the case of a liquid crystal matrix display, this characteristic is represented by the ratio of the voltage applied to the optical contrast on the screen.
Multiplexing in a matrix display is facilitated by the addition of a non-linear, electronic element (diode, transistor), arranged in series with the electrode of the elementary display point of the liquid crystal. The non-linear element makes it possible to introduce a threshold on the electrooptical characteristic of the effect used.
FIG. 1a diagrammatically shows in simplified manner, the organisation of a prior art, non-redundant, matrix display. The screen 1 of the display is formed by m rows and n columns of elementary display points 2 forming a matrix.
The video signal 3 is stored in capacitive samplers 4.sub.1 . . . 4.sub.n, which store one image row. The samplers are controlled by a shift register 5.sub.j in which circulates a pulse controlling the successive sampling operation. The video information contained in the sampler is transferred into the row of the corresponding matrix, where the control transistors of the elementary display points are in the conductive state. These transistors are controlled by the row control registers 6.sub.1 . . . 6.sub.n. The shift registers 5.sub.1 . . . 5.sub.n and the row control registers 6.sub.1 . . . 6.sub.m are controlled by clock rows 7 and 8 respectively.
A row-by-row scanning is performed in order to reproduce the video signal of the display, in accordance with a conventional method used in television equipment.
FIG. 1b shows an elementary display point of a liquid crystal display.
Electrode 9 is located on the face of the display in contact with the liquid crystal. A transparent electrode covering the complete screen is located on the front face of the liquid crystal. This electrode is kept at a constant potential and can e.g. be connected to earth 11. The two electrodes form a capacitance 10, the liquid crystal being located between the two electrodes.
A transistor 12 is connected in series with electrode 9, its drain being connected to the interconnection line 14 of a column, its grid being connected to an interconnection line 13 of a row of display points. Transistor 12 is the non-linear element authorizing the multiplexing of the electrodes 9 forming the matrix.
In such a matrix of components, such as a matrix display, the presence of defects with respect to the electronic components, the interconnection lines between the components or in the circuits controlling the rows and columns of the matrix leads to overall operational disturbances.
The most harmful defects in a matrix are interruptions of the interconnection lines between the electronic components and short-circuits between the rows and columns. For example, these defects are due to over or underetching of the interconnection lines during the matrix production process, or to the presence of grains of dust on a mask during the photolithography stage during the production of the matrix.
It is also possible for short-circuits to occur at the control transistors in the electronic components. Defects solely relating to a single elementary display point in a matrix display can be accepted, if the point is sufficiently small to be invisible to the naked eye.
An interruption of an interconnection line between the electronic components of the matrix or a short-circuit, however, makes the row or the row and the column respectively inoperative. Thus, complete defective rows make the matrix unusable.
Hitherto, most of the matrix displays produced were too small for most applications, but too large for the matrix of electronic components to be produced with a good production efficiency.
The efficiency of a matrix is dependent on the number and type of defects which can be accepted. For example, in a matrix of (240).sup.2 components and accepting defective rows, columns and elementary display points, the efficiency is approximately 50%, but such a circuit cannot be used. If only the defective elementary display points are accepted, the production efficiency decreases to 10%. The matrix is usable if the points are sufficiently small.
Without any defect, the efficiency can drop to 1% and can vary as a function of the technology used, but overall the results remain inadequate.
In order to obviate such problems and increase the production efficiency of these matrixes, it is possible to introduce a redundancy on several matrix levels.
Thus, it is possible to provide interconnection lines between the redundant electronic components, or there is a redundancy for each component, i.e. the number of components is increased.
Consequently, if one interconnection line is defective, it can be replaced by another formed by a redundant line, or in the second case it is possible to replace a defective component by another adjacent component.
The production of a matrix of redundant electronic components in accordance with the prior art consists of producing the components and the interconnections, then testing the continuity of the interconnection lines, bringing about a reconfiguration of the matrix by disconnecting the defective elements and reconnecting the satisfactory elements to one another and connecting the thus obtained matrix of electronic components to associated control circuits, which are located in the periphery of the matrix.
In order to be able to carry out the matrix operating test, all the redundant functions must be individually accessible during the test. The latter requires a large number of access hubs in the matrix.
This leads to an increase in the overall dimensions within the matrix, which is prejudicial to certain applications, e.g. in the case of a liquid crystal display. Moreover, it is necessary to mechanically displace the test points, which makes the testing process long and difficult.
According to the prior art, following the testing of the matrix, the satisfactory rows and columns are connected to the associated control circuits, which do not have any redundancy. Thus, it is not possible to test both the satisfactory operation of the complete control circuitry and the matrix. These post-test connections can lead to a deterioration of the functions recognised as satisfactory during the test.